Identification cards, typified by the ubiquitous plastic credit card are wallet-sized, planar plastic cards. Each card of this type bears a magnetic stripe and an area of embossed alphanumeric indications oriented along axes aligned with the long dimension of the card. The magnetic and embossed areas contain customer identification numbers which are sensed when the card is moved through a reader. In some instances, the magnetic stripe includes coded areas which can be incremented and decremented by a reader-writer terminal such as is used with some card-accessed subway systems.
A major problem with these cards is that they can be counterfeited, thus permitting unauthorized persons to use the account fraudulently. Losses due to such unauthorized use now exceed one billion dollars annually in the United States alone. No inexpensive approach is available to insure that a card is not counterfeit.